According to a recent National Geographic article, astronauts returning home after longer missions suffer permanently impaired vision. This is a problem that must be addressed in hard-science worlds if realism is desired - yet it is often overlooked.

Some of the other problems associated with microgravity are easier to deal with - muscle atrophy can be reversed by exercise, bone can be replaced or strengthened over time, the immune system can heal, coordination comes back, and cancer (from radiation exposure) is treatable.

But how do you prevent vision from becoming permanently impaired?

Context of the ConditionFrom the article linked at the top

Called "visual impairment intracranial pressure"

Not fully reversible (even by surgeries) when you get back to Earth

Occurs when cerebrospinal fluid builds up behind the eyes, which happens when gravity is reduced

Eyeballs are literally "flattened"

The solution scientists have proposed is "clunky" and entails being hooked into a machine to draw fluid throughout the body

Criteria for Solutions

Artificial gravity would fix the problem but it is not and will not
be present for all (if any) missions; it will not be accepted

Will optimally be noninvasive (tubes running into the skull aren't great) but this is not a necessity

Should be portable (being hooked into a large machine might help, but when mining asteroids or traversing the moon, there really isn't time)

5 Answers
5

Centrifuge looks like an answer, and actually was used in few books I've read. Fluid builds up due to lack of force pulling it down, right? It does not mind if that force is not strictly gravity.

First solution is to build ring-shaped living area. Even for relatively small craft, I'd say at least 10m diameter, centrifuge could simulate gravity well enough to prevent build up of the fluid. Coriolis effects would be weird, but ultimately fluids would be pulled down, and that's what we need.

Another one would be sessions in one-man centrifuge at 2 or 3G, just to draw fluid that accumulated between these sessions. This is less convenient for the crew, but also more portable.

Our bodies doesn't have any mechanism for sucking liquid from behind our eyes, except the gravity-based. This leaves us with centrifuges, and things that won't work:

Needles, like Eye Anesthesia Retrobulbar block, but sucking instead of injecting. Not practical due to build up of scars and high risk of infection. Not to mention eye damage if it's fellow miner performing this on you.

Pipe implanted there permanently. Bad for eyeball muscles, high risk of infection, risk of not sucking enough or sucking too much.

Pipe implanted, but going via different route. High risk of infection and complicated implanting. A tiny bit better than pipe on the front, but still really far from safe, and shares most of the risk.

Drugs - but there is no mechanism drugs could stimulate. For now these drugs are in the realm of fiction. Not yet science-fiction.

$\begingroup$@Zxyrra It seems that using a one-person, higher speed centrifuge to treat eye problems might be more of a medical solution rather than artificial gravity.$\endgroup$
– kingledionDec 3 '16 at 17:01

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$\begingroup$@Zxyrra what kingledion says. One man centrifuge is only thrice as big as hospital bed. Of course you can't always have it, but that's true for most medical procedures.$\endgroup$
– MołotDec 3 '16 at 17:17

$\begingroup$One-person centrifuge is portable. can be moved by one person even under Earth gravity. You didn't define "portable", so I assumed common "can be moved by one person or small team".$\endgroup$
– MołotDec 3 '16 at 22:27

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$\begingroup$Centrifugal force on such a small scale is hardly a gravity simulation, and you only asked for portable, changing it to "really small" only now. One man centrifuge is smaller than most mining equipment anyway! And passive you just added. If you are narrowing/changing your criteria, ask another question$\endgroup$
– MołotDec 4 '16 at 8:35

You could look at alternative treatments involving eye exercises. Mainstream doctors are often unaware of the work done by behavioural optometrists.

I have used the techniques in the book Natural Vision Improvement with surprisingly good results (but of course my issues were not caused by microgravity displacing cerebrospinal fluid - I am just suggesting this as an avenue for finding a possible treatment.)

There is also a body of knowledge from India (with all the caveats about lack of controlled studies). I know someone who was able to correct reasonably significant myopia using something similar to these techniques, but he eventually decided it was not worth doing the hour a day of yoga practices - it was easier to put on glasses!

However, if the distortion of the eye shape was caused by fluid movement, rather than the original shape of the eye, then these practices (along with headstand, which is not on the list I referenced above) could theoretically displace the fluid back to where it should be, and then you wouldn't have to keep spending an hour a day practising these techniques for the rest of your life.

$\begingroup$This is a very promising answer; I'm not sure if rotating the eye can decrease the pressure behind it but perhaps there's a way. +1$\endgroup$
– ZxyrraDec 3 '16 at 14:18

$\begingroup$Possibly these techniques work because they are performed in gravity, but this requires verification to be at all certain. The mediation techniques though might be independent of gravity.$\endgroup$
– a4androidDec 4 '16 at 5:25

For a story that needs to mention this, just have them take drugs while in space designed to address it. If increased pressure is the problem, then the same treatments used today for other causes of that condition ought to work.

update:

Since the available drugs that would suggest themselves have been tried and don’t work, some new drug would need to be found in time for your story.

You can remark that it was developed soon after long-duration missions started, or go into a backstory on how it required long duration mice studies in space, to discover the underlying mechanism well enough to start targeting drugs.

you could go with a mechanical solution, there are lots of things that you can't do in microgravity, or they are very difficult, set up stations where these needs can be met. for the eye a flexible microscopic tube could be inserted under the eyelid and through the fatty tissue around the eye and used to draw out the fluid periodically. It will be scary and uncomfortable but if you are in space you are already dealing with both of those, you can't do it forever, but you can't have people in microgravity forever either.

Honestly microgravity causes so many problems periodically spending time in artificial gravity, via centrifuge or other means, may really be the only solution. They will have to have gravity eventually, fluid build up around the heart, they eyes develop cataracts form the radiation, and breeding is impossible in microgravity.

You either A. have alter humanity, either genetically or a frankenstein's monster of surgeries and implants that won't be permanent fixes anyway, or B. provide the conditions humanity need, those really are your only options if you want hard science.

An option is to cancel out the microgravity by simply adding iron pieces to astronaut's suit and a magnetic field (on the ship), or charged suit (DC) and a electric field.
I prefer having gravity based on 2001: A Space Odyssey, good reference to hard science fiction. Circular ship, gravity generated by circular motion. But you dislike of artificial gravities and stuff.
You seems to be looking for hard science fiction here, but a it is difficult to answer as it is not a solved problem even on real life.

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